MIT develops PU-based, shape-changing foam

These are two 3D-printed, flexible scaffolds. On the left, the scaffold has been treated with a cool, rigid wax coating and maintains a rigid, bent position. Right, the uncoated scaffold collapses under the weight of a wrench.

CAMBRIDGE, Mass.—Engineers at Massachusetts Institute of Technology have developed a polyurethane-based material that they say could be used to create shape-changing robots.

MIT said in a news release that wax and foam-phasing changing material could facilitate surgical robots for operating inside the body without damaging organs or shape-changing robots that can squeeze through tight spaces on search and rescue missions.

Lead researcher Anette Hosoi said the challenge was to create a material that could be soft but also exert a reasonable amount of force on its surroundings.

“You can't just create a bowl of Jell-O, because if the Jell-O has to manipulate an object, it simply deforms without applying significant pressure to the thing it was trying to move.”

Researchers placed polyurethane foam in a bath of melted wax then squeezed the foam to encourage it to soak up the wax, which could be replaced by a stronger material such as solder.

To study the material's properties in more detail, the team printed a second version of the foam lattice structure in 3D, allowing them to control the position of each of the struts and pores, MIT said.

Officials at the institution said that running a wire along each of the coated foam struts and applying a current to heat up and melt the surround wax caused the material's hard outer shell to become soft and pliable.

“This would also repair any damage sustained,” said Hosoi. “This material is self-healing so if you push it too far and fracture the coating, you can heat it and then cool it, and the structure returns to its original configuration.”

The MIT team worked with researchers from the Max Planck Institute, Stony Brook University and Google-owned robotics firm Boston Dynamics as part of the Chemical Robots program of the government's Defense Advanced Research Projects Agency.